运输类飞机典型货舱地板下部结构冲击吸能特性

为了研究运输类飞机货舱地板下部结构在冲击载荷作用下的吸能特性，选取三框两段典型货舱地板下部结构试验件开展落重冲击试验，即质量为478.5 kg的落重以3.95 m/s的速度垂直冲击倒置并固定在测力平台上的试验件，分析试验件失效模式及动态响应，同时建立有限元模型进行仿真与试验结果相关性分析及吸能特性研究。结果显示，在此种工况的冲击载荷作用下，中间支撑件发生由32框面向34框面方向的弯曲，并带动机身框发生同向弯曲和扭转，从而导致C型支撑件发生与中间支撑件相反方向的弯曲变形，并最终在机身框与C型支撑件的连接处形成两处塑性铰；紧固件失效以位于中间支撑件附近区域的长桁和剪切角片连接处的22个扁圆头铆钉发生剪切失效为主；试验初始加速度峰值和初始撞击力峰值分别为25.1g和173 kN。仿真与试验获得的结构变形模式吻合较好，仿真获得的最大压缩量与试验结果24.3 mm相差3.7%，仿真获得的压板上初始加速度峰值与试验结果25.1g相差4%。通过仿真分析发现机身框和中间支撑件是主要的吸能部件，吸能贡献分别占总吸能的32.1%和30.4%。

Energy-absorbing characteristics of a typical sub-cargo fuselage section of a transport category aircraft

To study the crash characteristics of a typical sub-cargo fuselage section under impact load, a crash test is carried out with a three-frame and two-span sub-cargo fuselage section specimen. To study its failure modes and dynamic responses, the test specimen is upside down on a force measuring platform, and the mass of 478.5 kg impacted the test specimen vertically at the speed of 3.95 m/s. Also, a finite element model is established to analyze the correlation between the test and the simulation results and to study the energy absorption characteristics. The results show that the middle stanchions of the three frames are uniformly bent from 32 frame to 34 frame, and the fuselage frames are caused to bend and twist in the same direction, thereby causing the C-channel stanchions to undergo bending deformation in the opposite direction to the middle stanchions and finally forming two plastic hinges at the joint of the fuselage frames with the C-channel stanchions. The failure of the fasteners is mainly caused by the shear failure of 22 flat head rivets at the joint of the stringers and shear webs in the vicinity of the middle stanchions. The peak values of initial acceleration and impact force are 25.1g and 173 kN. The simulation results are well correlated with the test results. The deformation mode of simulation is in good agreement with the experimental results. The maximum compression displacement obtained by simulation is 3.7% different from the test result 24.3 mm, and the peak value of initial acceleration obtained by simulation is 4% different from the test result 25.1g. The simulation analysis finds that the fuselage frames and the middle stanchions are the main energy absorbing components, and the energy absorption contribution accounts for 32.1% and 30.4% of the total energy absorption.